Packet-based conversational service for a multimedia session in a mobile communications system

ABSTRACT

An important objective for third generation mobile communications systems is to provide IP services, and a very important part of these services will be the conversational voice. The conversational voice service includes three distinct information flows: session control, the voice media, and the media control messages. In a preferred embodiment, based on the specific characteristics for each information flow, each information flow is allocated its own bearer with a Quality of Service (QOS) tailored to its particular characteristics. In a second embodiment, the session control and media control messages are supported with a single bearer with a QoS that suits both types of control messages. Both embodiments provide an IP conversational voice service with increased radio resource efficiency and QoS.

Priority is claimed from U.S. provisional application Ser. No.60/354,483 filed Feb. 8, 2002, the disclosure of which is incorporatedhere by reference.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to commonly-assigned U.S. patent applicationSer. No. 09/985,573, entitled “Media Binding to Coordinating Quality ofService Requirements for Media Flows in a Multimedia Session with IPBearer Resources,” filed Nov. 5, 2001; and U.S. patent application Ser.No. 09/985,631, entitled “Method and Apparatus for Coordinating Qualityof Service Requirements for Media Flows in a Multimedia System With IPBearer Resources,” filed Nov. 5, 2001; U.S. patent application Ser. No.10/038,770, entitled “Method and Apparatus for Coordinating End-to-EndQuality of Service Requirements for Media Flows in a MultimediaSession,” filed Jan. 8, 2002; U.S. patent application Ser. No.10/*******, entitled “Processing Different Size Packet Headers for aPacket-Based Conversational Service in a Mobile Commnunications System,”filed Jan. **, 2003, the disclosures of which are incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to Internet Protocol (IP) multimediacommunications in a mobile network where time-sensitive services, suchas voice, are effectively and efficiently supported.

BACKGROUND AND SUMMARY

Fixed IP networks were originally designed to carry “best effort”traffic where the network makes a “best attempt” to deliver a userpacket, but does not guarantee that a user packet will arrive at thedestination. IP networks need to support various types of applications.Some of these applications have Quality of Service (QoS) requirementsother than “best effort” service. Examples of such applications includevarious real time applications (IP telephony/voice, video conferencing),streaming services (audio or video), or high quality data services(browsing with bounded download delays). Recognizing these QoSrequirements, the Internet Engineering Task Force (IETF), which is themain standards body for IP networking, standardized a set of protocolsand mechanisms that enable IP network operators to build QoS-enabled IPnetworks. But these protocols and mechanisms where designed with fixed,wire-line networks in mind. New and different challenges face IPcommunications in mobile, wireless communication networks.

Quality of service is important for providing end users with satisfyingservice. The efficient use of the radio resources is also important toensure maximum capacity and coverage for the system. Quality of servicecan be characterized by several performance criteria such as throughput,connection setup time, percentage of successful transmissions, speed offault detection and correction, etc. In an IP network quality of servicecan be measured in terms of bandwidth, packet loss, delay, and jitter.

Consider for example an IP telephony session between User-A and User-Bwhere User-A accesses an IP backbone through a local access, mobilecommunications network In wireline communications, a local accessnetwork is often a Public Switched Telephone Network (PSTN) or anIntegrates Services Digital Network (ISDN). But for communicationsinvolving a mobile radio, the local access network must include a radioaccess network Example mobile communication networks include the GlobalSystem for Mobile communications (GSM) or the Universal MobileTelecommunications System (UMTS) network User-B is similarly connectedto the IP network through a local access network, and both users may notuse the same type of access network The IP backbone network includes anumber of IP routers and interconnecting links that together provideconnectivity between the IP network's ingress and egress points andthereby make two party communication possible.

As far as the users are concerned, the perceived quality of servicedepends on the service provided both in the local access networks and onthe IP backbone network Of particular interest is the specific casewhere at least one of the access networks is a mobile communicationsnetwork like a or GSM/GPRS network The radio interface in such a networkis the most challenging interface in the communication in terms ofdelivering a particular quality of service.

An objective of third generation mobile communications systems, likeUniversal Mobile Telephone communications System (UMTS), is to providemobile radios with the ability to conduct multimedia sessions where acommunication session between users may include different types ofmedia. Perhaps the most important medium to support in multimediasessions is voice. There is a need for more resource-efficient,packet-based conversational (e.g., voice) multimedia services. Althoughthe idea of conversational IP services is desirable, a practicalimplementation of a conversational IP service requires overcomingseveral technical hurdles before the idea becomes a commercial reality.Conversational IP services should deliver high speech quality both interms of fidelity and low delay. Connection set up and serviceinteraction times should be reasonably fast. Indeed, packet-based voiceservice should be comparable to circuit-switched traditional voicetelephony. The radio spectrum must be used efficiently. Services mustcover a wide geographic area and be able to service. roaming users.Because voice is only one component in a multimedia session, it shouldbe established and disconnected independently from the session.

There are three distinct information flows to be considered for aconversational IP voice service. Each flow affects the overallperformance of the IP voice service. For example, the voice media flowis crucial when it comes to providing high speech quality. The sessioncontrol flow is important when it comes to service set-up times/delays,and the media control protocol is primarily used to monitor media flowsand provide information allowing the synchronization of different mediaflows.

In addition, network operators must be able to provide theconversational IP service at a reasonable cost. Although fixed,wire-line access networks like LAN's permit over-provisioning, wirelessnetworks cannot afford that luxury because of limited radio bandwidthand the need to support user mobility. An objective of the presentinvention is to provide an efficient way to transport these threeinformation flows.

The three information flows have different needs and characteristics.Quality of Service (QoS) parameters of special importance to sessionsignaling include bit rate, delay, and priority. Session signaling ismostly low volume with a small average bandwidth demand. But thetransmission rate still needs to be fairly high to reduce delay. Delaytime is also influenced by bearer-handling delays and retransmissionsover the air interface. Under heavy load conditions, session signalingshould get priority. The session signaling should not be put on a bearerthat carries a large volume of user data because the session signalingcan pot then be prioritized above the user data, resulting in undesireddelays. Therefore, in accordance with one aspect of the invention, thesession signaling is transported using a separate packet data “context”between the mobile terminal and a packet-based access network with aninteractive class of QoS. This session signaling packet data context issupported by a dedicated bearer with an interactive class of QoS.Logical connections, like a packet data context, a radio access bearer,a radio bearer, etc., are generally referred to as “bearers.”

The voice media packets carry regularly-generated voice samples, e.g.,every 20 ms, and each packet has a relatively small payload size. Thosevoice packets must be received by the remote terminal with the sametiming, e.g., every 20 ms, in order to have a reasonable voice quality.Both objectives are met in accordance with another aspect of the presentinvention where the voice media flow is transported using a separatepacket context between the mobile terminal and a packet-based accessnetwork with a conversational class of QoS. The voice media packets aresupported by a dedicated bearer with a conversational class of QoScharacteristics.

Compared to voice media packets, voice media control message packets areconsiderably larger in size and are sent less frequently, e.g., everyfew seconds. But there is no strict delay or jitter requirement likethere is for voice packets. For media control message packets, aconversational radio access bearer would waste radio resources.Alternatively, transporting the media control message packets on thesame radio access bearer as the voice packets would delay the voicepackets causing a disruption in speech. To mitigate this problemrequires allocating more resources to a single bearer than would beneeded for two bearers. So in accordance with another aspect of theinvention, the media control signaling is transported using a separatepacket data “context” between the mobile terminal and a packet-basedaccess network with an interactive class of QoS. This media controlsignaling packet data context is supported by a dedicated bearer with aninteractive class of QoS characteristics.

Thus, in a preferred embodiment, each of these three information flowsrequired for a conversational IP voice service is allocated its ownbearer and packet data context with a QoS class tailored to thecharacteristics of each flow. In this way, high quality, packet-basedvoice service can be provided with radio resources being efficientlyallocated in accordance with the particular needs for the differentinformation flows.

In a second embodiment, the session signaling and the voice mediacontrol messages share a single radio bearer with an interactive classof QoS characteristics. As in the first embodiment, the voice mediapackets are supported by a dedicated bearer with a conversational classof QoS characteristics. Because the session signaling load normally isheavy during the session setup and the voice media control message loadnormally picks up after the session is setup, one interactive QoS bearersupports both the session setup signaling and the voice media controlsignaling. Although there may be some delays whenever there isoverlapping session signaling and voice media control signaling requiretransmission at the same time, those delays may be an acceptabletradeoff to reduce the number of bearers by one.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of the presentinvention may be more readily understood with reference to the followingdescription taken in conjunction with the accompanying drawings.

FIG. 1 illustrates a communications system in which a multimedia sessionmay be established between a mobile terminal and a remote host;

FIG. 2 illustrates in block format various functions performed by themobile terminal, access point, and multimedia system;

FIG. 3 is a high level diagram showing three separate bearers forsupporting a packet-based voice session;

FIG. 4 Illustrates a GPRS/UMTS-based communication system for conductingmultimedia sessions;

FIG. 5 is a high level diagram showing three separate bearers forsupporting a packet-based voice session from the mobile terminal to theIMS interface in a GPRS/UMTS access network;

FIG. 6 is a flowchart illustrating example procedures for establishing amultimedia session with packet-based, voice IMS service; and

FIG. 7 is an example signaling diagram showing a mobile terminalattaching to the network, establishing a primary PDP context and asession signaling RAB, and registering with the IMS in a GPRS/UMTSaccess network;

FIGS. 8A-8C illustrate example signaling message exchanges forestablishing dedicated RABs for a voice media packet stream and mediacontrol messages as part of establishing a multimedia session withpacket-based, voice IMS service.

DETAILED DESCRIPTION

In the following description, for purposes of explanation and notlimitation, specific details are set forth, such as particularembodiments, procedures, techniques, etc. in order to provide a thoroughunderstanding of the present invention. However, it will be apparent toone skilled in the art that the present invention may be practiced inother embodiments that depart from these specific details. For example,in one example below, the present invention is described in an exampleapplication to a GSM/UMTS system. However, the present invention may beemployed in any access network.

In some instances, detailed descriptions of well-known methods,interfaces, devices, and signaling techniques are omitted so as not toobscure the description of the present invention with unnecessarydetail. Moreover, individual function blocks are shown in some of thefigures. Those skilled in the art will appreciate that the functions maybe implemented using individual hardware circuits, using softwarefunctioning in conjunction with a suitably programmed digitalmicroprocessor or general purpose computer, using an applicationspecific integrated circuit (ASIC), and/or using one or more digitalsignal processors (DSPs). This is true for all of the nodes describedbelow including mobile terminals and network nodes.

In the following description, a mobile terminal is used as one exampleof a user equipment (UE) allowing a mobile user access to networkservices. In a mobile radio communications system, the interface betweenthe user equipment and the network is the radio interface. Thus,although following description uses the term “mobile terminal,” thepresent invention may be applied to any type or configuration of userequipment that can communicate over a radio interface.

To realize a QoS with clearly defined characteristics and functionality,a bearer must be set up from the source to the destination of theservice that supports that QoS. A “bearer” is a logical connectionbetween two entities through one or more interfaces, networks, gateways,etc., and usually corresponds to a data stream. Non-limiting examples ofbearers used in the example embodiments below include a packet datacontext, a radio access bearer, and a radio bearer. A QoS bearer serviceincludes all aspects to enable the provision of a contracted QoS.Example aspects include the control signaling, user plane transport, andQoS management functionality.

To provide IP quality of service end-to-end from mobile terminal to aremote host, it is necessary to manage the quality of service withineach domain in the end-to-end path where each domain corresponds to aset of nodes utilizing the same QoS mechanisms. For purposes ofsimplifying the description, only the bearers and selected signalingemployed in establishing and maintaining a packet-based voice sessionfrom the mobile terminal up to the IP backbone network are described. Apacket-based voice session maybe a voice only call or a multi-media callwith a voice being one of the media. For purposes of illustration only,a multi-media session that includes a voice information flow isdescribed below, with only the voice part being described. The inventionmay be applied to IP voice communication that is not part of amultimedia session.

The invention may be employed, for example, in the simplifiedcommunications system shown in FIG. 1 where a Mobile Terminal (MT) 10may initiate and conduct a multimedia session with a remote host 20. Themobile terminal 10 is coupled to a radio access network (RAN) 12 overthe radio interface. The RAN 12 is coupled to an Access Point 15 in apacket-switched access network (PSAN) 14. If desired, the access point15 may function as a protocol proxy for the MT local host. The PSAN 14is coupled to a Packet Data Network (PDN) 18 to which the remote host 20is coupled via a local access network (LAN) 19. The basic traffic flowfor a multimedia session (shown as solid lines) between the mobileterminal 10 and remote host 20 is transported via these three networks12, 14, and 18. The PSAN 14 and the PDN 18 communicate multimediacontrol signaling (shown as dashed lines) to an IP Multimedia System(IMS) 16 that can be separate from or an integral part of the PacketData Network 18.

To provide further details regarding setting up a multimedia sessionbetween the MT 10 and the remote host 20, reference is now made to FIG.2. The mobile terminal 10 includes Access Network Bearer Control 40coupled to multimedia session control 42. The Access Network BearerControl block 40 transports internal bearer control signaling, which isnot dedicated to a particular session, to an Access Network BearerControl block 46 in the Access Point 15 transparently through the radioaccess network over a PDN signaling transport bearer. Both AccessNetwork Bearer Control blocks 40 and 46 assist in establishing a packetaccess bearer for setting up the session shown as the pipe entitled“transport of session signaling.” Over this bearer, the mobile terminal10 initiates a multimedia session including a plurality of media datastreams with the remote terminal 20. Each media data stream or “flow” istransported over a corresponding packet access bearer illustrated as a“transport of media flow” pipe coupled to a Forward Media Streams block44 in the mobile terminal. Two media flows 1 and 2 are shown forpurposes of illustration in this multimedia session. The multimediasystem 16 in the packet data network 18 employs a Route Media Streamsblock 50 to route the packets in each media flow between the mobileterminal 10 and the remote terminal/host 20. Multimedia system 16includes a Session Control block 48 that utilizes session signaling fromthe MultimedialSession Control block 42 in the mobile terminal 10 tocorrelate each multimedia flow and its corresponding quality of servicerequirements with the session to establish necessary admission rules forthe session.

For a session involving voice IMS services, there are at least threeinformation flows that must be transported between the mobile terminaland the network: session control messages, the voice media itself, andvoice media control messages. The three information flows have differentneeds and characteristics. QoS parameters of special importance tosession signaling include bit rate, delay, and priority. Each of thethree information flows required for a conversational IMS voice serviceis allocated its own bearer with a QoS class tailored to thecharacteristics of each flow. In a preferred, example embodiment, eachinformation flow is allocated a packet data context and a supportingradio access bearer both having the appropriate QoS.

Because of its mostly low volume with a low, average bandwidth demand,its need for low delay (including bearer handling delays andretransmissions over the air interface), and its need for priority inheavy load conditions, the session signaling is transported using apacket data context and a radio access network bearer that both supportan interactive class of QoS characteristics. The interactive classprovides a maximum bit rate, delivery order, maximum data unit size, aresidual bit error ratio, delivery of erroneous data units, and priorityhandling.

The strict periodicity required for voice packets, e.g., one every 20ms, the relatively small payload size of each voice packet, and the needfor the remote terminal to receive those packets at the sameperiodicity, e.g., every 20 ms, in order to have a reasonable voicequality led the inventors to transport the voice media flow using apacket data context and a radio access network bearer that both supporta conversational class of QoS characteristics. The conversational classprovides a maximum bit rate, guaranteed bit rate, minimum transferdelay, delivery order, maximum data unit size, a residual bit errorratio, and delivery of erroneous data units.

In contrast, the voice media control message packets are considerablylarger in size and are sent less frequently, e.g., every few seconds.But there is no strict delay or jitter requirement like there is forvoice packets. A conversational radio access bearer would wasteresources. Transporting the voice media control message packets on thesame radio access bearer as the voice packets would delay the voicepackets causing a disruption in speech. To mitigate that problemrequires allocating more resources to a single bearer than would beneeded for two bearers. Having similar needs as the session signaling,the media control signaling is transported using a packet data contextand a radio access network bearer with an interactive class of QoScharacteristics.

FIG. 3 illustrates the three application flows—session controlsignaling, voice media, and media control signaling—each being supportedfrom the mobile terminal 10 to the remote host 20 over the RAN 12, thePSAN 14, the IMS 16, the PDN 18, and the local access network (LAN) 19.This separate support allows each application flow to be supported witha quality of service tailored to its specific needs while as the sametime ensuring that limited resources are used efficiently in providingthat service.

The invention may also be employed in a more specific (but non-limiting)example of a multimedia session set up via a local General Packet RadioService (GPRS)/Universal Mobile Telecommunication System (UMTS)-basedaccess network 22 shown in FIG. 4. The local GPRS/UMTS network 22includes a set of network elements between the local host UE-A,corresponding to a Mobile Terminal (MT), and an external packetswitching network the user is connecting to, like the Internet. Theradio access network (RAN) 28 provides access over the radio interfaceto/from the MT and includes radio base stations (RBSs) and radio networkcontrollers (RNCs). The RAN 28 is coupled to a GPRS packet accessnetwork 30 that includes a supporting Gateway GPRS Support Node (SGSM)32 and a Gateway GPRS Support Node (GGSN) 34. The GGSN 34 providesinterworking between the GPRS/UMTS network 22 and the IP backbonenetwork 24. The coupling (shown as a solid line) between the GPRS/UMTSnetwork 22 and the IP backbone network 24 is used to transport user dataIP packets.

The local GPRS/UMTS-type network 22 is coupled to an IP multimediasystem (IMS) 36. Communication with the IMS 36 (shown as dashed lines)permits exchange of multimedia session control-related messages. The IMS36 is typically a part of (although it may be separate from and coupledto) an IP backbone network 24. The remote host corresponding to mobileterminal UE-B is coupled to the IP backbone network 24 through its homecellular network 26, and by signaling connection, to the IMS 36.

The mobile terminal UE-A desires to establish a multimedia session withUE-B. The packet traffic for this session follows the solid linecouplings between the various nodes. The session is established with andmanaged by the IP Multimedia System IMS) 36. The IMS 36 messages arebased on IP application signaling, which in a preferred, exampleembodiment includes session initiation protocol (SIP) and sessiondescription protocol (SDP). SIP is a signaling protocol to establishsessions, and SDP is a text-based syntax to describe the session andincludes, for example, the definition of each media stream in thesession. The IP multimedia system 36 includes one or more Call StateControl Functions (CSCFs) 38.

Before the mobile terminal can send packet data to the remote host, themobile terminal must “attach” to the GPRS network to make its presenceknown and to create a Packet Data Protocol (PDP) “context” to establisha relationship with a GGSN. The PDP context is a bearer between themobile terminal and the GGSN. The PDP attach procedure is first carriedout between the mobile terminal and the SGSN to establish a logicallink. As a result, a temporary logical link identity is assigned to themobile terminal. A PDP context is established between the mobileterminal and a GGSN selected based on the name of the external networkto be reached. One or more application flows may be established over asingle PDP context through negotiations with the GGSN. An applicationflow corresponds to a stream of data packets distinguishable as beingassociated with a particular host application. Example application flowsinclude voice packets carrying digitized (and usually coded) voicesamples, an electronic mail message, a link to a particular InternetService Provider (ISP) to download a graphics file from a web site, etc.One or more application flows may be associated with the same mobilehost and the same PDP context.

Within a GPRS/UMTS access network, radio network resources are managedon a per PDP context level, which corresponds to one or more userflow/data streams and a certain QoS class. A PDP context is implementedas a dynamic table of data entries, comprising all needed informationfor transferring PDP data units between the mobile terminal and theGGSN, e.g., addressing information, flow control variables, QoS profile,charging information, etc. The PDP context signaling carries therequested and negotiated QoS profile between the nodes in the UMTSnetworks It has a central role for QoS handling in terms of admissioncontrol, negotiation, and modifying of bearers on a QoS level.

FIG. 5 illustrates the mapping between radio bearer (MT-RNC), radioaccess bearer (MT-SGSN), and PDP context (MT-GGSM. The relationshipbetween a radio access bearer and a PDP context is a one-to-one mapping.A radio access bearer is mapped onto one or more radio bearers. Thethree IP packet flows—session signaling, voice, and media control—aretransported through the UTRAN using separate radio bearers, radio accessbearers, and PDP contexts. As indicated in FIG. 3 in parentheses,example session control signaling that may be used in this exampleembodiment is Session Initiation Protocol (SIP) messages carryingSession Description Protocol (SDP) information over User DatagramProtocol (UDP). The voice packets may be carried in this example by theReal-Time Transport Protocol (RTP) protocol over UDP, and the controlmessages associated with the voice packets are Real-Time ControlProtocol (RTCP) messages over UDP. Of course, other protocols andformats may be used.

Three separate PDP contexts corresponding to separate radio accessbearers (RABs) and separate radio bearers (RBs) are established for thethree voice IMS service flows, as described above. The QoS associatedwith the SIP/SDP session signaling PDP context/RAB/RB(s) is aninteractive QoS class suited for a request/response pattern ofcommunication which need to have its payload content preserved. The RTPvoice media PDP context/RAB/RB(s) is a conversational QoS class suitedto preserve the time relation between information entities of thestream. The RTCP voice media control signaling PDP context/RAB/RB(s) isan interactive QoS class.

FIG. 6 illustrates example procedures in flowchart form (entitled BearerSupport for Voice IMS) for establishing the three bearers for a voice MSsession. The mobile terminal establishes an initial connection with thepacket access network and registers with the IMS. A primary “session”PDP context is established over an interactive QoS class, session radioaccess bearer (RAB). Session signaling messages are conveyed over thatRAB (block 100). A multimedia session is initiated by or with the mobileterminal over the session RAB requesting establishment of a voice orconversational IMS service (block 102). A secondary “media” PDP contextis established with a conversational QoS class, media RAB to transportmedia (voice) packets (block 104). A secondary “media control” PDPcontext is established with an interactive QoS class, media control RABto transport (block 106). Once set up, the session continues (block108).

A way to improve the overall PDP context establishment time would be toperform combined PDP context establishments. Establishing the PDPcontexts related to the media and the media control could be combinedinto one procedure. This combined PDP context establishment may befacilitated by introducing PDP context request and accept messages thatallow for more than one PDP context.

Example signaling to establish a primary PDP context and register withthe IMS for the system in FIG. 4 is shown in FIG. 7. Briefly, the MTsends a Radio Resource Control (RRC) Connection Request to the RNC,which responds with an RRC Connection Setup message. The MT sends anAttach Request to the SGSN via the RNC, which responds with severalauthentication, ciphering, and security mode requests. After the MTsatisfies those requests, the SGSN sends an Attach Accept message to theMT.

At this point, the MT sends an Activate PDP Context Request message tothe SGSN, which includes a requested QoS profile. The SGSN sends a“Create PDP Context Request” to the GGSN carrying the QoS profile. Basedon this profile, an admission control is performed at the GGSN level,and the GGSN may restrict the QoS if, for example, the system isoverloaded. The GGSN stores the PDP context in a database. The GGSNreturns the negotiated QoS to the SGSN in a “Create PDP ContextResponse” message, and the SGSN stores the PDP context in its database.The SGSN sends a “RAB Assignment Request” to the RNC in the RAN toestablish a radio access bearer (RAB) service to carry the RAB QoSattributes. For the session signaling, a RAB with an interactive QoS isrequested. From the interactive class QoS attributes, the RNC determinesthe radio-related parameters corresponding to the QoS profile, e.g.,transport format set, transport format combination set, etc. The RNCsends a “Radio Bearer Set-up” message to the MT. When the RAN and the MTare ready to transfer traffic, a Radio Bearer Setup Complete message issent to the RNC and a “RAB Assignment Complete” message, is sent to theSGSN. The negotiated QoS, here an interactive QoS class, is sent fromthe SGSN to the MS in an “Activate PDP Context Accept” message.

Once the primary PDP context is activated and the corresponding RAB andRBs are set up, the MT registers with the IMS. The MT sends a SIPRegister message via the primary PDP context and corresponding bearersto the IMS. The IMS responds with a SIP 401 Unauthorized message. If theuser is not registered, the 401 message is sent to the user including achallenge. The user includes the response to the challenge in the nextregister message, and the CSCF checks the response. If the response iscorrect, the CSCF knows the user is authentic. The MT repeats theRegister message, and the IMS responds with a SIP 200 OK messageindicating that the MT is registered with the IMS and may initiate (orparticipate in) a multimedia session.

An example signaling flow diagram for an example conversational IMSsession between a mobile terminal MT1 and a remote MT2 is shown in FIGS.8A-8C Initially, and as explained above in FIG. 7, MT1 establishes afirst PDP context with the GGSN to be supported by a session signalingbearer needed to establish the multimedia session. The MT1 sends a SIPINVITE message on the signaling bearer to the IMS to setup theconversational IP multimedia session. The INVITE message includes thesession details regarding the number of media flows and requestedcorresponding quality of service. The IMS authenticates MT1 as asubscriber and authorizes the session. The SIP INVITE message isforwarded to MT2 via external networks. MT2 confirms the session requestin a SIP “183” Progress message returned to the IMS. The SIP 183 is anacknowledgement message to the SIP INVITE message. The IMS confirms thesession, and delivers a session ID in a SIP 183 Progress message to theMT1. SIP PRACK and 200 OK PRACK acknowledgement messages are exchangedbetween the MT1 and MT2 via the IMS so that a session may established.

In order to establish a PDP context and corresponding bearer for themedia (voice) application flow for the session, MT1 sends and activatesa second PDP context request message via RNC to the SGSN. The SGSN sendsa Create PDP Context Request to the GGSN, and the GGSN returns a CreatePDP Context Response message. Each PDP context message includes arequest for a conversational class quality of service. The SGSN thensends an RAB Assignment Request to the RNC requesting a conversationalRAB. A Radio Bearer Setup message is sent from the RNC to MT1, and MT1responds with a Radio Bearer.Setup Complete message. The RNC thenforwards an RAB Assignment Response message to the SGSN, which returnsan Activate Secondary PDP Context Accept message specifying aconversational quality of service. A similar set of procedures forestablishing a secondary PDP context, corresponding RAB, andcorresponding radio bearers is performed by MT2 with its local accessnetwork nodes.

Both MT1 and MT2 then perform similar procedures to establish asecondary PDP context and corresponding radio access bearers for mediacontrol packets for the session as indicated by the second brace in FIG.8. However, in this message exchange, the PDP context messages specifyan interactive quality of service and the RAB assignment messages willspecify an interactive RAB.

With the session PDP contexts and bearers with their desired quality ofservices established, the mobile terminals MT1 and MT2 exchange SIPmessages indicating that both MT1 and MT2 are ready to proceed withtheir conversation. During the session, if the voice and voice controlstreams are inactive for a period of time, the corresponding radioaccess and radio bearers may be released to conserve radio resources.But the session radio access bearer and radio bearer(s) are preferablymaintained for the life of the session. This facilitates establishinganother session involving MT1.

In a second, “two bearer” embodiment, the session signaling and thevoice media control messages share a single radio bearer with aninteractive class of QoS. As in the first embodiment, the voice mediapackets, (e.g., RTP), are supported by a dedicated bearer with aconversational class of QoS. The session signaling load, (e.g., SIPsignaling), normally is heavy during the session setup, and the voicemedia control message load, (e.g., RTCP), picks up after the session issetup. Although not identical, both streams carry signaling information.This time division and characteristic similarity permit sharing a singlebearer. One interactive QoS bearer (preferably high priority) supportsboth the session setup signaling and the voice media control signaling.There may be some delays whenever both session signaling and voice mediacontrol signaling require transmission at the same time. One example ofsuch a delay would occur when a service is added, dropped, or changed inthe middle of the session. Such delay, however, may be an acceptabletradeoff in order to reduce the number of bearers by one.

A session may include media in addition to voice, e.g., text, video,etc. Each additional media has its own media and media control flowsthat require additional PDP context and radio access bearers. One way todo this is to activate a new PDP context for each additional media flowand media control flow. There may be situations where all the RTCP flowsmay be multiplexed onto a single PDP context without loosing muchquality. Alternatively, all RTCP flows could be multiplexed onto thesame PDP context as the SIP signaling. Although this would impactperformance, it may be an acceptable compromise in some situations.

With the present invention, conversational IP voice services can beprovided which deliver high speech quality both in terms of fidelity andlow delay because each information flow is supported with a quality ofservice that meets its specific needs and only uses the radio resourcesaccording to its specific needs. While the present invention has beendescribed with respect to particular embodiments, those skilled in theart will recognize that the present invention is not limited to thesespecific example embodiments. Different formats, embodiments, andadaptations besides those shown and described as well as manyvariatiops, modifications, and equivalent arrangements may also be usedto implement the invention. The invention is limited only by the scopeof the claims appended hereto.

1-53. (canceled)
 54. A method for establishing a session involving amobile radio terminal configured to access a packet-based access networkvia a radio access network, comprising: establishing a first bearerextending between the mobile terminal and the packet-based accessnetwork; using the first bearer to initiate a session that includes apacket-based voice communication and to carry one or more sessionmessages for implementing a packet-based voice service; establishing asecond bearer for the session extending between the mobile terminal andthe packet-based access network and carrying voice packets associatedwith the packet-based voice service; and using the first bearer to carrycontrol messages associated with the packet-based voice service.
 55. Themethod in claim 54, wherein each of the first and second bearers isestablished with a quality of service tailored to characteristics of theinformation being carried over that bearer.
 56. The method in claim 54,wherein the first bearer is established with an interactive quality ofservice and the second bearer is established with a conversationalquality of service.
 57. The method in claim 54, further comprising:establishing a priority for the first bearer.
 58. The method in claim54, wherein the first and second bearers correspond to first, second,and third packet data contexts, respectively.
 59. The method in claim54, wherein the first and second bearers are radio access bearers(RABs).
 60. The method in claim 59, further comprising: establishing afirst Packet Data Protocol (PDP) context for session messages relatingto the packet-based voice service and for control messages associatedwith the voice packets; mapping the first PDP context onto the firstRAB; establishing a second PDP context for voice packets; and mappingthe second PDP context onto the second RAB.
 61. The method in claim 60,wherein the session messages are Session Initiation Protocol (SIP)messages carrying Session Description Protocol (SDP) information over aUser Datagram Protocol (UDP), the voice packets are carried by theReal-Time Transport Protocol (RTP) protocol over UDP, and the controlmessages associated with the voice packets are Real-Time ControlProtocol (RTCP) messages over UDP.
 62. A node for use a mobilecommunications system that includes in a packet-based access network,comprising electronic circuitry configured to perform the followingtasks related to establishing an IP session: coordinate with a mobileradio terminal to establish a first bearer extending between the mobileradio terminal and the packet-based access network configured toestablish the IP session including a conversational IP service and tocarry one or more session messages for implementing the conversationalIP service; coordinate with the mobile radio terminal to establish asecond bearer for the IP multimedia session extending between the mobileradio terminal and the packet-based access network to carry voicepackets associated with the conversational IP service; and coordinatewith the packet-based access network node to configure the first bearerto carry control messages associated with the conversational IP service.63. The node in claim 62, wherein the bearers are packet data contexts.64. The node in claim 62, wherein the bearers are radio access bearers(RABs).
 65. The node in claim 64, wherein the node is a Serving GPRSSupport Node (SGSN) in a General Packet Radio Services (GPRS) network,and wherein the SGSN electronic circuitry is configured to: map a firstPDP context onto the first RAB; map a second PDP context onto the secondRAB; and map a third PDP context onto the first RAB.
 66. The node inclaim 62, wherein the node is a mobile radio terminal or a fixed networknode.
 67. The node in claim 62, wherein the first bearer is establishedwith an interactive quality of service and the second bearer isestablished with a conversational quality of service.
 68. The node inclaim 62, wherein the session messages are application control SessionInitiation Protocol (SIP) messages carrying Session Description Protocol(SDP) information over User Datagram Protocol (UDP), the voice packetsare carried by the Real-Time Transport Protocol (RTP) protocol over UDP,and the control messages associated with the voice packets are mediacontrol Real-Time Control Protocol (RTCP) messages over UDP.
 69. Thenode in claim 62, wherein the session is a multimedia session and theelectronic circuitry is further configured to establish an additionalbearer for a session media flow other than the voice packets.